1. Field of the Invention
The present invention relates to an stacked electrical connector, and more particularly to stacked electrical connectors with improved signal transmission.
2. Description of Related Art
Universal Serial Bus (USB) is used widely in variety electric devices as a standard and simple interface. As of 2006, the USB specification was at version 2.0 (with revisions). The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Previous notable releases of the specification were 0.9, 1.0, and 1.1. Equipment conforming to any version of the standard will also work with devices designed to any previous specification (known as: backward compatibility).
USB mentioned above supports three data rates respectively as follows: 1) A Low Speed rate of up to 1.5 Mbit/s (187.5 KB/s) that is mostly used for Human Interface Devices (HID) such as keyboards, mice, and joysticks; 2) A Full Speed rate of up to 12 Mbit/s (1.5 MB/s). Full Speed was the fastest rate before the USB 2.0 specification and many devices fall back to Full Speed. Full Speed devices divide the USB bandwidth between them in a first-come first-served basis and it is not uncommon to run out of bandwidth with several isochronous devices. All USB Hubs support Full Speed; 3) A Hi-Speed rate of up to 480 Mbit/s (60 MB/s).
However, as the development of electric industry, even the USB 2.0 can not satisfied the requirement of many electric devices. For example, under a circumstance transmitting an audio or video file, which is always up to hundreds MB, even to 1 or 2 GB, currently transmission rate of USB is not sufficient. As a consequence, faster serial-bus interfaces are being introduced to address different requirements. PCI Express, at 2.5 GB/s, and SATA, at 1.5 GB/s and 3.0 GB/s, are two examples of High-Speed serial bus interfaces.
However, these non-USB protocols, such as PCI Express which is useful for its higher possible data rates, a 26-pin connectors and wider card-like form factor limit the use of Express Cards, and SATA which uses two connectors, one 7-pin connector for signals and another 15-pin connector for power, are not used as broadly as USB protocols. Many portable devices are equipped with USB connectors other than these non-USB connectors. One important reason is that these non-USB connectors contain a greater number of signal pins than an existing USB connector and are physically larger as well, especially in a stacked electrical connector. Due to its clumsiness, the PCI Express and SATA connector can not adapt to the development trend of gently, thin, short and small size.
USB connector is soldered on a circuit board of an computer usually. The USB 2.0 A type connector according to USB-IF usually comprises an insulative housing with a tongue plate extending forwardly, four contacts retained in the insulative housing and a metal shield. Each contact has a contact portion extending to a lower side of the tongue plate and exposing out thereof flexibly. The contact portion presents as arc type and can move along a thickness direction of the tongue. The four contacts comprise a power contact, a ground contact, a − data contact and a + data contact. The − data contact and + data contact present as a pair of differential signal contacts which are located between the power contact and the ground contact. The metal shield encloses the tongue plate and forms a first receiving space for receiving a USB plug.
Hence, an stacked electrical connector which is based USB interface, but has a high signal transmission and a simple structure, is desired to overcome the disadvantage of the prior art.